In recent years, the installation of surveillance cameras in stores, shopping districts, apartment complexes or the like and of drive recorders in commercial vehicles has become common. The number of cases where moving images are used as evidence is increasing. To deal with troubles when dealing or customer support is carried out over the phone, it has become almost a common practice to record conversations between customers and operators and store them as evidence.
These days, video tapes and image and audio files are offered without change when moving images and audio are used as evidence. However, as more images and audios are stored in digital format, it becomes easier to alter and edit the images and audios. Therefore, verification by third parties, such as signature or time stamp, is required when the images and audios are used as evidence. Services or products to tape or record the voices of telephone operators along with time stamps are actually on sale. Demand for such techniques is expected to grow over the years ahead.
Meanwhile, as the number of surveillance cameras or the like increases, there are problems with privacy protection for the use of taken images. Debates are going on in the Ministry of Internal Affairs and Communications and the like.
Due to the enforcement of the Personal Information Protection Law and the like, there are stringent restrictions on the use of individual's privacy information. Disclosure, partial deletion or the like is required at the request of the identical person.
For such problems as meeting the requirements of both evidence and privacy protection, what goes on is the research on a technique for sanitizable signatures to ensure the partial originality (integrity) of a portion of a digital document and to conceal (sanitization).
In particular, what is disclosed in International Publication Pamphlet No. WO2006/08847 is a sanitizable signature technique for digital documents to solve the problem that a signature put on a document may not be examined because the document is partially concealed (the present technique is referred to as PIAT, hereinafter). The application of the above PIAT enables the signature to be examined even for the sanitized digital document to which the signature is added and also allows a third party to verify that any portions other than the sanitized portion (where modification and addition are possible) is not altered.
However, the problem with International Publication Pamphlet No. WO2006/08847 is that when a portion of large-size data (long video and audio) such as moving image or audio is extracted, the amount of information related to the signature is large.